The main body of the St Mary's Church was built in the late 12th century and was probably rebuilt in the 1240s, including a tower, porches and north aisle, after being damaged by Llewelyn the Great in 1220. An upper level of clerestory windows was added during the 15th century. The tower originally had a timber spire clad in lead, though it was removed in 1802 after becoming dangerous.
The church's interior has a fine timber panelled ceiling with moulded beams, rafters and ribs, and carves bosses at the intersections. It dates to c. 1500.
The church organ dates from 1737, by Harris & Byfield, with two keyboards.
References:Visby Cathedral (also known as St. Mary’s Church) is the only survived medieval church in Visby. It was originally built for German merchants and inaugurated in 1225. Around the year 1350 the church was enlarged and converted into a basilica. The two-storey magazine was also added then above the nave as a warehouse for merchants.
Following the Reformation, the church was transformed into a parish church for the town of Visby. All other churches were abandoned. Shortly after the Reformation, in 1572, Gotland was made into its own Diocese, and the church designated its cathedral.
There is not much left of the original interior. The font is made of local red marble in the 13th century. The pulpit was made in Lübeck in 1684. There are 400 graves under the church floor.